Constructing four-in-one catalysts to realize ultralow voltage hydrogen production at ampere-level current densities†

Abstract

An anion exchange membrane water electrolyzer (AEMWE) is emerging as key technology for hydrogen production. However, its widespread application requires further reduction of cost and improvement of efficiencies. Here, we synthesize a four-in-one catalyst (V_SA-CoN_x) to achieve high-efficiency coupling hydrogen production by combining with the hydrazine oxidation reaction (HzOR) and the urea oxidation reaction (UOR). The as-synthesized V_SA-CoN_x exhibits excellent performance in all the four reactions of HzOR, UOR and hydrogen/oxygen evolution reactions (HER/OER). The HER–HzOR coupling system only requires an ultra-low voltage of 0.21 V to deliver an ampere-level current density (1 A cm⁻²), while the conventional HER–OER AEMWE needs nearly an input of 1.88 V. Remarkably, this HER–HzOR coupling system largely reduces the energy expenditure of the AEMWE by approximately 90%, which hits a record in the low energy cost for all water electrolysis systems known to date. Given the energy consumption of the traditional AEMWE of approximately 4.56 kW h Nm⁻³ of H₂ at a current density of 1 A cm⁻², the HER–HzOR AEM electrolyzer only requires 0.51 kW h Nm⁻³ of H₂. This HER–HzOR coupling system not only significantly lowers the energy expenditure of large-scale H₂ production but also addresses the hydrazine-associated environmental pollution.